The proposed work consists of a study of some of the mechanisms that regulate the secretion of ACTH and TSH. Of particular current interest are the hypothalamic and pituitary roles of prostaglandins and cyclic AMP in this regard. In conjunction with these studies, hypothalamic cholinergic systems will be investigated further insofar as they relate to the regulation of pituitary secretion. Another major endeavor will concern the site(s) and mechanism(s) of the feedback regulation of TSH secretion by T3 and T4. Finally, several of the interactions between the adrenocortical axis and the thyroid axis are to be studied. Whenever possible, the experiments are performed using unanesthetized, unstressed animals. A central theme of this work is to study these endocrine systems as dynamic systems, in that we will be examining time courses of responses rather than single points in time, amine turnover rates rather than static concentrations, secretion rates rather than blood concentrations of hormones, etc. Fluorometric and radioimmune assays are used in conjunction with stereotaxic microinjection of hypothalamus or anterior pituitary and chronic catheterization techniques.